There is a need for an angle of arrival laser detection system that provides a wide field of view and that can resolve the direction of incident laser illumination to less than a degree in both elevation and azimuth. Currently, there are non-coherent laser detectors that have a large field of view (2 Pi Steradians). These systems use both imaging and non-imaging optics. In systems using imaging optics, use is made of multiple apertures with lenses to focus the incoming laser light and display the image (a spot) on a focal plane to determine the X, Y and Z coordinates. These focused systems provide good resolution, but require lenses and sufficient signal processing to convert a focused spot into X, Y, and Z components, and then into polar coordinates. The primary disadvantage of these systems is their cost and complexity.
In the systems which are non-imaging, a single detector element is placed in each aperture to detect incident radiation. Comparison between the received energy from adjacent apertures is then converted into a digital count that represents the energy at each aperture and an algorithm similar to that used in mono-pulse radar is used to define the direction of the source of maximum energy intensity. While the non-imaging systems are simpler than imaging systems, the resolution is not as good as the focussed system, and signal processing requires analogue to digital conversion, and then a comparison with the received signal power from adjacent apertures to compute the direction of maximum received power. Current systems which use this technique can resolve the direction of an incident laser source to some degree, but the signal processing technique is a multi-step process in that the incident energy through each of a plurality of adjacent apertures is first detected in an analog detector; then each analog signal is digitalized; all of the digital outputs from the adjacent apertures are then compared to determine the "best fit" resultant, which is then used to determine the direction vector of the source of maximum intensity. There are several disadvantages to this approach. First improved resolution requires multiple overlapping apertures, and in addition, the signal processing techniques that are required are susceptible to intensity modulations that could cause false results. As a result of using amplitude comparison techniques, these variations will then result in increased error in determining the correct direction vector.